Meh, the Vikings island hopped a couple of hundred miles and got to the northernmost part of America. Sailing close to the equator (like the Mediterraneans and the Polynesians did) is much more impressive
The cave-dwelling part was hyperbole, of course. My main point was that northern Europe was decidedly under-developed for the majority of human history. Despite having very impressive civilizations close to it for thousands of years.
I'm not claiming genetic inferiority either. I'm just saying that history wasn't over in 1,500 BC when the Egyptians were the most advanced in the world. It wasn't over in 1,000 AD when the Muslims were, and it's not over now, when Europeans have been ruling the world for 500 years.
A look at history suggests the most obvious: we're all more or less genetically equal when it comes to intelligence. Development and industrialization vary by era and tell very little.